Trips: Ponderosa Pine Forests Out West

I am back in one of my favorite ecosystems, ponderosa pine forests in the mountainous areas of the west, and it’s like I never left – everything’s exactly the same. Ponderosa pine forests are an interconnected system of organisms who have been doing this together for a long, long time, and they’re getting very good at it. Ignore the cat – she’s always getting onto my photographs.

Haviland Lake, Colorado. The glacier was here, obviously.

Ponderosas were familiar to me from my drive-by vacations back when I was still working, but in our first full year of retirement, 2011, I finally got the chance to get out the lawn chair and observe this ecosystem over several days, and I was struck with how specific to the place each member of the community was. Then I started reading about it, and I was REALLY amazed. These things are a thousand piece jigsaw puzzle, and everything fits together in an interlocking manner.

Here’s one that has had an exciting life, judging by the strange branch off to the right down low.

Let’s start with the hosts, the ponderosas. As their name tells you, they’re a BIG tree for the dry west. They top out at 268 feet over in the Oregon rain forest, making them the tallest known pine, but even in the arid southwest they hit 100 feet easily. The pine needles are 4-6 inches long and a yellowish rather than bluish green, and the trunks are distinctive in mature trees, with flat reddish-brown areas where the top of the bark has shed away, separated by dark fissures. Younger trees have darker trunks. And they smell wonderful, and make that great wind-in-the-trees noise when the wind picks up. I usually sit out in the desert in the early spring long enough to be very glad to see a tree once I get up here, and these ponderosas are getting to be old friends.

Ponderosa Range Map by Robert Z. Callaham courtesy Wikipedia. Each subspecies has its own mountainous area.

All the light green area was pine forest 14,000 years ago. Map courtesy Arizona State University.

Ponderosas are distributed in a highly altitude- and latitude-dependent pattern throughout the Rockies, and divided up into a number of subspecies with longer and shorter needles, etc. by their geographical isolation from each other, but it wasn’t always this way.

Fourteen thousand years ago, the entire southwest was a vast pine forest, and as the climate warmed up and dried out, this monolithic mass of coniferous forest fragmented into the altitude islands we see today. The pines abandoned the lowlands, which are all desert now, and live at specific altitude ranges, higher in the south and lower in the north. You don’t really need an altimeter out here. As you drive uphill the scrub junipers appear at 5000 feet, and when you climb past 6000 feet, you start seeing the big guys, the ponderosas.

Abert’s squirrel. They do not pose for photographs.

Specific to these forests is a really striking squirrel, Abert’s squirrel, whose ancestors had the run of the entire western Ice Age forest, but followed the trees uphill and now have their own analogous subspecies in each separate ponderosa area, forever marooned on their altitude island. These squirrels are almost the size of my cat, and have these hilarious tasseled ears, which Fiona the Fearless wants to nibble on, but will never get the chance. Guess what the Abert’s squirrel eats? Ponderosa pine cones, bark, and buds. Darn right they followed the trees uphill.

Here’s the fungus, normally invisible inside the branches but producing fruiting bodies and spores for the squirrels to track all over the place in May.

And it gets weirder – there’s a fungus which lives on the ponderosa tree branches. It doesn’t really hurt the tree, but does affect branch growth, producing many small twisted branches that form a ball in the tree. Guess where the Abert’s squirrels nest? In the branch concentrations, protected from the elements, and unintentionally spreading the spores throughout the forest every time they go out, making more nest balls for more squirrels next year. There’s another ectomycorrhizal fungus that grows on the tree roots, extending their reach and bringing water and minerals to the root in exchange for the tree’s carbohydrates. The fruiting bodies of this fungus are a favorite squirrel food, which when they defecate spreads spores throughout the forest, benefiting more trees, and squirrels, and fungi. See? Everyone here gets a cut of the action. It’s all interconnected.

As I spend more time here I’m going to try to figure out how the birds and other animals fit into the jigsaw puzzle. I have time. This forest has been here for a long, long time, and will be here for a while longer. Maybe there’s a place for me to fit in here, too.